With the RU9, Cayin has entered the fifth generation of Nutube application. The Gen5 Nutube Timbre circuit features a refined three-stage amplification architecture. Cayin engineers have meticulously designed and fine-tuned the negative feedback (NFB) loops to deliver distinct Nutube 6P1 vacuum tube timbres, while also integrating the Dual Tube Timbre feature first introduced in Gen3—offering users a seamless blend of dual tube warmth and solid-state precision.

Both 3.5mm and 4.4mm PO/LO outputs support two switchable Tube Timbres and a Solid-State Timbre.

• Classic Tube Timbre: No large-loop NFB; each stage operates independently through local feedback, and the overall gain determined by the cumulative gain of each stage. Distortion characteristics closely resemble classic tube amplifier, resulting in a higher THD value. The sound signature exhibit a classic vacuum tube amplifier, with relatively more thermal noise and a richer presentation. 
• Modern Tube Timbre: A large-loop NFB circuit will determine the total gain. By incorporating NFB over multiple amplification stages, the THD will be reduced significantly.
  The harmonic distortion characteristics and sound signature lean more towards a modern style, with greatly reduced thermal noise and a slightly cleaner tube sound.
• Solid-state Timbre: Built with op-amps and precision-tuned peripheral circuits. Delivers accurate resolution, fast dynamics, and neutral tonality.

Custom-designed anti-vibration module for the Nutube tube, featuring an FPC flexible PCB, a custom silicone damping sleeve, and a pin suspension system. Engineered to eliminate microphonic interference.

Hyper Mode is automatically activated under DC Mode.

It further increases the amplifier's quiescent current and operating voltage, offering greater clarity, expansive soundstage, and punchier dynamics.

The Cayin RU9 offers three flexible power modes to suit a wide range of usage scenarios. Whether you're on the go or chasing peak performance, choose between:

• When USB IN is connected: Dongle Mode - ideal for compact "dongle-style" use.
• When POWER is connected:
  Battery Mode - system runs primarily on USB power, with internal battery providing backup support.
  DC Mode - full external power delivery with direct routing to the amplifier circuit, automatically activates Hyper Mode for maximum output.

Supports QC3.0 and PD2.0 fast charging protocols.

The Cayin RU9 features a magnetic attachment system, seamlessly attaching to compatible smartphones and tablets. A magnetic adapter ring and a custom magnetic leather case is included, handcrafted with precise cutouts.

Also included is an L-shaped USB interconnect cable. Shielded with a braided design for reduced signal loss.